Conventionally, poly-Si (polysilicon) or other semiconductor thin films are widely used for TFTs (Thin Film Transistors) and solar cells. A method for formation of those semiconductor thin films with low cost is one in which an amorphous silicon film is irradiated with laser light so as to be crystallized. Laser process can be applied also to, for example, activation of impurity atoms introduced to the semiconductor substrate by ion injection or plasma doping. However, this laser crystallization technique has such problems as occurrence of laser scanning traces and moreover requires quite expensive equipment.
Thus, there have been discussed techniques for continuously and inexpensively performing heat treatment of a processing-object substrate or the like by applying plasma irradiation via a slit-like opening to make plasma scanning in a direction perpendicular to a longitudinal direction of the opening (see, e.g., JP 2013-120633 A, JP 2013-120684 A, JP 2013-120685 A, and T. Okumura and H. Kawaura, Jpn. J. Appl. Phys. 52(2013)05EE01).
For example, an inductively coupled plasma torch having an opening for plasma irradiation involves some contrivance for facilitating ignition of plasma. It is noted that the term ‘ignition’ herein refers to generation of a plasma from a no-plasma state. Accordingly, there have conventionally been discussed various ignition methods. In a plasma processing apparatus described in JP 61-68900 A as an example, a cylindrical chamber for plasma generation is set to a vacuum internal state so as to facilitate the plasma ignition. As another example, a plasma processing apparatus described in JP 2002-343599 A employs an ignition-use coil other than a coil for plasma generation. As a further example, a plasma processing apparatus described in JP 3-67496 A is so designed that a high voltage is applied to a metal rod placed within a chamber to ignite a plasma.
With the constitution that a plasma is generated in a space (chamber) between a high-potential conductor member and a low-potential conductor member, as in the plasma processing apparatuses described in JP 2013-120633 A, JP 2013-120684 A and JP 2013-120685 A, it is possible to implement stable plasma ignition under atmospheric pressure without using the plasma ignition methods described in above-mentioned JP 61-68900 A, JP 2002-343599 A and JP 3-67496 A.